Try nullable.

selekt-java/src/jmh/kotlin/com/bloomberg/selekt/cache/benchmarks/LinkedLruCacheBenchmark.kt

@@ -28,10 +28,12 @@ import org.openjdk.jmh.annotations.State
 @State(Scope.Thread)
 open class LinkedCacheInput {
     internal lateinit var cache: LinkedLruCache<Any>
+    internal lateinit var largeCache: LinkedLruCache<Any>
 
     @Setup(Level.Iteration)
     fun setUp() {
         cache = LinkedLruCache(1) {}
+        largeCache = LinkedLruCache(64) {}
     }
 }
 
@@ -48,4 +50,11 @@ open class LinkedLruCacheBenchmark {
         get("1") {}
         get("2") {}
     }
+
+    @Benchmark
+    @BenchmarkMode(Mode.Throughput)
+    fun getEntries(input: LinkedCacheInput) = input.largeCache.run {
+        get("1") { "" }
+        get("2") { "" }
+    }
 }

selekt-java/src/jmh/kotlin/com/bloomberg/selekt/cache/benchmarks/StampedCacheBenchmark.kt

@@ -0,0 +1,51 @@
+/*
+ * Copyright 2024 Bloomberg Finance L.P.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.bloomberg.selekt.cache.benchmarks
+
+import com.bloomberg.selekt.cache.StampedCache
+import org.openjdk.jmh.annotations.Benchmark
+import org.openjdk.jmh.annotations.BenchmarkMode
+import org.openjdk.jmh.annotations.Level
+import org.openjdk.jmh.annotations.Mode
+import org.openjdk.jmh.annotations.Scope
+import org.openjdk.jmh.annotations.Setup
+import org.openjdk.jmh.annotations.State
+
+@State(Scope.Thread)
+open class StampedCacheInput {
+    internal lateinit var cache: StampedCache<Any>
+
+    @Setup(Level.Iteration)
+    fun setUp() {
+        cache = StampedCache(1) {}
+    }
+}
+
+open class StampedCacheBenchmark {
+    @Benchmark
+    @BenchmarkMode(Mode.Throughput)
+    fun getEntry(input: StampedCacheInput) = input.cache.run {
+        get("1") {}
+    }
+
+    @Benchmark
+    @BenchmarkMode(Mode.Throughput)
+    fun getEntryWithEviction(input: StampedCacheInput) = input.cache.run {
+        get("1") {}
+        get("2") {}
+    }
+}

selekt-java/src/main/kotlin/com/bloomberg/selekt/cache/CommonLruCache.kt

@@ -18,61 +18,65 @@ package com.bloomberg.selekt.cache
 
 class CommonLruCache<T : Any>(
     @PublishedApi
+    @JvmField
     internal val maxSize: Int,
     disposal: (T) -> Unit
 ) {
     @PublishedApi
-    internal var cache: Any = StampedCache(maxSize, disposal)
+    @JvmField
+    internal var cache: StampedCache<T>? = StampedCache(maxSize, disposal)
+    @PublishedApi
+    @JvmField
+    internal var linkedCache: LinkedLruCache<T>? = null
 
     fun evict(key: String) {
-        when (val cache = cache) {
-            is StampedCache<*> -> cache.evict(key)
-            is LinkedLruCache<*> -> cache.evict(key)
-            else -> error("Unrecognized cache class: {}")
+        cache?.let {
+            it.evict(key)
+            return
         }
+        linkedCache!!.evict(key)
     }
 
     fun evictAll() {
-        when (val cache = cache) {
-            is StampedCache<*> -> cache.evictAll()
-            is LinkedLruCache<*> -> cache.evictAll()
-            else -> error("Unrecognized cache class: {}")
+        cache?.let {
+            it.evictAll()
+            return
         }
+        linkedCache!!.evictAll()
     }
 
-    @Suppress("UNCHECKED_CAST")
-    inline fun get(key: String, supplier: () -> T): T = when (cache) {
-        is StampedCache<*> -> (cache as StampedCache<T>).let {
-            it.get(key) {
+    inline fun get(key: String, supplier: () -> T): T {
+        cache?.let {
+            return it.get(key) {
                 supplier().also { value ->
                     if (it.shouldTransform()) {
                         // Adding another entry to the cache will necessitate the removal of the
                         // least recently used entry first to honour our maximum size constraint.
                         // For the implementation of the store currently assigned, this is an O(N)
                         // operation. We transform to an O(1) implementation.
                         transform()
-                        (this@CommonLruCache.cache as LinkedLruCache<T>).store.put(key, value)
+                        linkedCache!!.store.put(key, value)
                     }
                 }
             }
         }
-        is LinkedLruCache<*> -> (cache as LinkedLruCache<T>).get(key, supplier)
-        else -> error("Unrecognized cache class: {}")
+        return linkedCache!!.get(key, supplier)
     }
 
-    fun containsKey(key: String) = when (val cache = cache) {
-        is StampedCache<*> -> cache.containsKey(key)
-        is LinkedLruCache<*> -> cache.containsKey(key)
-        else -> error("Unrecognized cache class: {}")
+    fun containsKey(key: String): Boolean {
+        cache?.let {
+            return it.containsKey(key)
+        }
+        return linkedCache!!.containsKey(key)
     }
 
     @PublishedApi
     internal fun StampedCache<T>.shouldTransform() = (store.size >= maxSize)
 
     @PublishedApi
     internal fun transform() {
-        (cache as StampedCache<*>).asLruCache().also {
-            cache = it
+        linkedCache = cache!!.asLruCache().also {
+            cache = null
         }
     }
 }

selekt-java/src/test/kotlin/com/bloomberg/selekt/cache/CommonLruCacheTest.kt

@@ -16,6 +16,7 @@
 
 package com.bloomberg.selekt.cache
 
+import org.junit.jupiter.api.Assertions.assertNull
 import org.junit.jupiter.api.Test
 import org.junit.jupiter.api.assertThrows
 import org.mockito.kotlin.anyOrNull
@@ -28,6 +29,7 @@ import org.mockito.kotlin.times
 import org.mockito.kotlin.verify
 import org.mockito.kotlin.whenever
 import kotlin.test.assertFalse
+import kotlin.test.assertNotNull
 import kotlin.test.assertSame
 import kotlin.test.assertTrue
 import kotlin.test.fail
@@ -44,6 +46,7 @@ internal class CommonLruCacheTest {
         val cache = CommonLruCache(1, disposal)
         cache.get("1") { first }
         assertSame(first, cache.get("1") { fail() })
+        assertNotNull(cache.cache)
     }
 
     @Test
@@ -53,6 +56,7 @@ internal class CommonLruCacheTest {
         cache.get("2") { second }
         assertSame(first, cache.get("1") { fail() })
         assertSame(second, cache.get("2") { fail() })
+        assertNotNull(cache.cache)
     }
 
     @Test
@@ -62,6 +66,7 @@ internal class CommonLruCacheTest {
         cache.get("2") { second }
         assertFalse(cache.containsKey("1"))
         assertSame(second, cache.get("2") { fail() })
+        assertNull(cache.cache)
     }
 
     @Test
@@ -83,8 +88,8 @@ internal class CommonLruCacheTest {
         cache.get("2") { second }
         cache.evictAll()
         inOrder(disposal) {
-            verify(disposal, times(1)).invoke(same(first))
             verify(disposal, times(1)).invoke(same(second))
+            verify(disposal, times(1)).invoke(same(first))
         }
     }